Many work vehicles use hydraulics to control certain functions performed by the vehicle. For example, many work vehicles, such as four wheel drive articulated loaders, use hydraulics to control a variety of functions, such as steering, loading, and braking. Many such work vehicles utilize load sensing systems. A load sensing system varies the pump flow and fluid pressure to meet a load requirement and has one hydraulic function which has preference over other hydraulic functions. For example, the steering function of vehicle may have priority over the hydraulic function which controls the movement of an attachment bucket. In such load sensing systems, a priority valve is typically used to assure that the priority function, such as steering, always has available fluid. Such systems are typically sized such that the required flow for the priority function, such as maximum steering, is not met until mid throttle of the engine. This often results in poor steering performance at low idle of the engine.
According to an illustrative embodiment of the disclosure, a vehicle includes an articulated frame having a front portion and a rear portion, and a plurality of traction devices configured to propel the frame on the ground. A steering assembly includes a hydraulic steering actuator operably coupled to the front portion and the rear portion of the frame. A loader assembly includes a hydraulic loader actuator supported by the frame. A priority pump is in fluid communication with the steering assembly. A first compensator valve is in fluid communication with the priority pump, and a second compensator valve is in fluid communication with the priority pump and is coupled in parallel with the first compensator valve. The first compensator valve and the second compensator valve are configured to provide fluid flow from the priority pump to the loader assembly only when fluid pressure from the pump exceeds a predetermined value.
According to a further illustrative embodiment of the disclosure, a vehicle includes an articulated frame having a front portion and a rear portion, and a plurality of traction devices configured to propel the frame on the ground. A control system includes a pump, at least one hydraulic steering actuator operably coupled to the front portion and the rear portion of the frame, and a steering valve configured to place the at least one hydraulic steering actuator in fluid communication with the pump. A first compensator valve is configured to control the flow of fluid from the pump to the steering valve by providing priority to the flow of fluid to the at least one hydraulic steering actuator. A pressure regulating valve is positioned intermediate the compensator valve and the steering valve, and is configured to regulate the pressure of fluid supplied to the steering valve.
According to another illustrative embodiment of the disclosure, a vehicle includes an articulated frame having a front portion and a rear portion, and a plurality of traction devices configured to propel the frame on the ground. A steering assembly includes a hydraulic steering actuator operably coupled to the front portion and the rear portion of the frame, and a steering valve fluidly coupled to the steering actuator. A loader assembly includes at least one loader actuator supported by the frame, and a loader valve fluidly coupled to the loader actuator. A priority pump is in fluid communication with the steering assembly. A first compensator valve is in fluid communication with the priority pump, and a second compensator valve in fluid communication with the priority pump and is coupled in parallel with the first compensator valve. A pressure regulating valve is positioned intermediate the first and second compensator valves and the steering valve. The pressure regulating valve is configured to regulate the pressure of fluid supplied to the steering valve. A load signal line is fluidly coupled to the steering assembly and is configured to transmit load pressure signals, generated by loads acting on the hydraulic steering actuator, to the first and second compensator valves. The first and second compensator valves are configured to sense a pressure differential between the fluid discharged from the priority pump and the fluid present in the load signal line, and to control fluid flow to the loader assembly in response to the pressure differential.
According to yet another illustrative embodiment, a vehicle includes an articulated frame having a front portion and a rear portion, and a plurality of traction devices configured to support the frame on the ground. A primary work circuit includes a hydraulic steering actuator operably coupled to the front portion and the rear portion of the frame. A secondary work circuit includes a hydraulic actuator supported by the frame. A pump is in fluid communication with the primary work circuit and is configured to supply a fluid flow. An engine is operably coupled to the pump and has an operating speed ranging from at least low engine speed to full throttle engine speed, the fluid flow varying based upon the operating speed of the engine. A manifold is in fluid communication with the pump and is configured to selectively provide fluid flow to the primary work circuit and the secondary work circuit based upon engine operating speed, such that the primary work circuit is supplied with adequate fluid flow to ensure full performance of the hydraulic steering actuator from low engine speed to full throttle engine speed.